Screening of Weissella bacterial strains for Production of Bioactive Metabolites on Different Substrates

Abstract

Lactic acid bacteria (LAB) have been recognized for their potential to hydrolyse different types of substrates, including plant-based proteins, releasing products of nutritional and biotechnological interest. This thesis investigated three Weissella strains, including AYR-17, AYR-1, and AYO-14, for their ability to grow on different substrates, break down proteins and produce bioactive metabolites. Bacterial growth was assessed on different substrates, including a protein-rich medium supplemented with glucose, a starch-rich potato medium, and MRS broth, which served as control. HPLC analysis revealed different organic acid profiles that varied with substrate and oxygen availability, consistent with the heterofermentative metabolism of these strains. Lactate was the dominant organic acid on MRS, reaching ~7.50-8.50 g/L under both conditions, whereas on the protein-glucose medium lactate was lower (approximately 2.60-5.0 g/L), and on potato it remained stable at ~0.5 g/L throughout cultivation. Aerobic cultivation favoured acetate production on both MRS (~6.0-8.0 g/L) and protein-glucose (~4.0-6.0 g/L), while anaerobic cultivation on MRS resulted in the higher concentration of ethanol (3.0-3.6 g/L). On potato, acetate remained at a constant level at approximately 4.0-4.3 g/L, suggesting carryover from the inoculum rather than production occurring. HPAEC-PAD analysis confirmed the strain’s ability to break down starch and synthesize glucose-rich heteropolysaccharides containing minor amounts of arabinose and galactose. Strain AYO-14 (anaerobic) exhibited growth-dependent EPS production, yielding 90.23 µg/mL, while strain AYR-17 (aerobic) exhibited growth-independent EPS production, with a yield of 157.04 µg/mL. Although o phthaldialdehyde (OPA) analysis indicated a net decrease in free amino groups during cultivation, further analyses are needed to determine the strains' ability to digest yellow pea protein. Overall, these findings suggest that when the strains utilise monosaccharide substrates, carbon is directed primarily toward acid fermentation, whereas on polysaccharide substrates such as starch, carbon is directed toward exopolysaccharide synthesis.

Popular Abstract

What if the bacteria used to ferment the foods we commonly eat, could also help us to better digest plant-based products and create healthier foods? In this project, Weissella strains were evaluated on different substrates (the raw material as a food source) to investigate their ability to digest plant proteins and produce bioactive compounds. Bioactive compounds are naturally occurring compounds with significant effect on biological processes that may be beneficial, and support health and reduce the risk of disease.
Fermentation has been used since time immemorial to preserve food and add a wide variety of flavors, but bacteria have shown they can do much more than that. Certain microorganisms can produce certain bioactive compounds that have been shown to improve food quality, optimize industrial processes and even support health.
This degree project focuses on Weissella, a group of lactic acid bacteria commonly found in fermented foods. Different Weissella strains were screened on various substrates, such as pea protein and potato, to investigate how growth conditions influence their metabolism and the production of useful compounds.
One of the most interesting findings was the production of acetic acid under aerobic conditions. Acetic acid is a well-known compound that gives vinegar its characteristic flavor, but it also plays some important biological and industrial roles. Increased acetate production can enhance bacterial growth and inhibit unwanted microorganisms during fermentation. It is also a valuable intermediate that can be used to produce other compounds relevant for future biotechnological and industrial applications. Understanding how bacteria regulate acetate production could, therefore, help optimize fermentation processes and improve production of valuable metabolites. Lactic acid was also produced, which is of importance due to its ability to improve food safety and shelf life, while also contributing to flavour and texture of fermented foods. In addition, lactic acid has industrial significance as a sustainable raw material for biodegradable plastics and other biobased products.
Another interesting finding was the production of exopolysaccharides (EPS) when potato waste was used as a substrate. EPS are natural polymers produced by bacteria that can improve the texture and stability of foods by acting as natural emulsifiers and thickeners. This makes them very interesting for applications in fermented and plant-based foods. Beyond their food properties, Some EPS have been shown to provide health benefits, including anti-inflammatory and probiotic properties. Lastly, potato waste represents an abundant by-product, and its valorisation as fermentation substrates decreases dependence on raw materials and contributes to sustainability by reducing food waste and promoting circular economy.
Overall, these results highlight the importance of understanding the metabolic behaviour of bacteria and how it can be tailored to produce desired compounds. Bacteria such as Weissella could contribute in the future to the development of foods and valuable compounds that are not only more sustainable, but also healthier and more functional.

• author: Fernández van der Veen, Esther and Cevapovic, Sena
• supervisor: Roya Sardari; Olena Prykhodko
• organization: Biotechnology (MSc); Biotechnology (M.Sc.Eng.)
• course: KBTM01 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: weissella, yellow pea protein, lactic acid bacteria (LAB), heterofermentative metabolism, exopolysaccharides (EPS), proteolytic activity, biotechnology
• language: English
• id: 9231075
• date added to LUP: 2026-08-11 09:23:09
• date last changed: 2026-08-11 09:23:09